Open-access content [Tanya Weaver](/authors/tanya-weaver) — Thu 3 Apr 2025
**Researchers at Northwestern University have developed a tiny pacemaker that is injected into the body, controlled using light shone through the skin, and dissolves when no longer needed.**
Temporary pacemakers are often required after heart surgery while the patient waits for a permanent pacemaker or to help restore the heart’s rhythm.
Implanting these devices requires invasive procedures, with wires protruding from the body. Potential complications include infection, dislodgement, torn or damaged tissues, bleeding and blood clots.
Researchers at Northwestern in Illinois, US, had previously developed a quarter-sized (24mm) dissolvable electronic device for temporary pacing that eliminated the need for bulky batteries and wires.
While it proved promising in pre-clinical animal studies, cardiac surgeons wanted the device to be even smaller so it could be used in newborn babies with congenital heart defects.
Bioelectronics engineer John A Rogers, who led the device development, said: “There’s a crucial need for temporary pacemakers in the context of paediatric heart surgeries, and that’s a use case where size miniaturisation is incredibly important.”
Experimental cardiologist Igor Efimov, who co-led the study, said: “About 1% of children are born with congenital heart defects. The good news is that these children only need temporary pacing after a surgery. In about seven days or so, most patients’ hearts will self-repair. But those seven days are absolutely critical.”
These devices were powered by near-field communication protocols that required a built-in receiver antenna, which limited miniaturisation of the device. So Rogers and his team had to use different technology. When the electrodes in the device, from two different metals, come into contact with surrounding biofluids in the body they form a battery delivering electrical pulses to the heart.
Rogers said: “The surrounding biofluids act as the conducting electrolyte that electrically joins those two metal pads to form the battery.”
The pacemaker is paired with a soft, wireless, wearable device mounted on the patient’s chest. An infrared wavelength of light penetrates the skin and muscles to detect the patient’s heart rate.
When it detects an irregular heartbeat, it automatically shines a light pulse to activate the pacemaker. The light then flashes on and off at a rate that corresponds to the normal heart rate.
Rogers said: “A very tiny light-activated switch on the opposite side from the battery allows us to turn the device from its ‘off’ state to an ‘on’ state upon delivery of light that passes through the patient’s body from the skin-mounted patch.”
According to the researchers, even though the pacemaker measures just 1.8mm in width, 3.5mm in length and 1mm in thickness, it still delivers as much stimulation as a full-sized pacemaker.
Rogers said: “The heart requires a tiny amount of electrical stimulation. By minimising the size, we dramatically simplify the implantation procedures, we reduce trauma and risk to the patient, and, with the dissolvable nature of the device, we eliminate any need for secondary surgical extraction procedures.”
The tiny pacemaker has shown promise in animal and heart models, and the team think it could also be used in other situations where electrical stimulation is needed, like the brain.
The study – ‘Millimetre-scale bioresorbable optoelectronic systems for electrotherapy’ – has been published in the journal _Nature_.
Below is a video of the team describing the pacemaker and its development.
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